1. Field of the Invention
The present invention relates to an image processing device and, more specifically, relates to an improvement in an emphasis processing in a digital type copying machine, an image scanner and the like when performing an edge emphasis processing for read data.
2. Background Art
In an image scanner and the like, an original image is developed into pixels, the gray levels of the respective pixels are read as gray level signals and the read signals relating to the image are outputted such as to a laser printer through a pseudo intermediate gradient processing of binary value data. In such case or in a case when an image is inputted and outputted in a digital type copying machine an edge emphasis processing or a nonuniformity correction processing for input image data is performed in order to obtain a high quality image. The pseudo intermediate gradient processing was invented by the present inventor and was already patented as U.S. Pat. No. 5,307,425.
In an edge emphasis processing, a gray level of a certain pixel, which is obtained via individual light receiving parts or light receiving elements arranged correspondingly to respective pixels, is detected as a gray level signal (normally an analog value) and a detected value (which is normally a digital value converted from the above analog value) of the noted pixel determined in accordance with the detected value is corrected by detected values of the pixels surrounding the noted pixel. For this purpose, it is necessary to refer to detected values of the pixels on scanning lines immediately before and after the current scanning line. Accordingly, a memory is necessary which stores these detected values (digital values) of the respective pixels as pixel data.
On the other hand, in these days a plurality of main scanning lines are simultaneously scanned by a single main scanning operation. In such instance, the pixel data (detected values of the respective pixels) on the scanning lines immediately before and after the current scanning line are normally stored simultaneously in the memory. However, for the edge emphasis of the last line among the plurality of main scanning lines, pixel data of the first line obtained in the subsequent main scanning operation is necessary, therefore the edge emphasis processing for the last line is required to wait until the pixel data of the subsequent first line is obtained. Further, for the edge emphasis of the first line in the subsequent main scanning operation the pixel data of the last line in the immediately before main scanning operation is necessitated, therefore the pixel data of the last line have to be preserved. For this reason, in such a scanner that reads image data by scanning a plurality of main scanning lines simultaneously, a memory is necessary which stores detected values of the pixels covering the last one line and the subsequent first one line.
FIG. 5 and FIGS. 6(a) and 6(b) are diagrams for explaining relationships between scanning operation and edge emphasis processing when a plurality of main scanning lines are simultaneously scanned by a single scanning operation.
As shown in FIG. 5, a scanner is provided with a CCD sensor 11 for 128 pixels (with regard to pixels see FIG. 6(a)) located in vertical direction (in the subscanning direction). Through a single scanning operation a main scanning covering 128 lines is simultaneously performed with a vertical width covering 128 pixels. After one main scanning operation has completed, the scanner moves in vertical direction (in the subscanning direction) by the width covering 128 pixels for the subsequent main scanning operation within return time in the retrace interval (see FIG. 5).
In an edge emphasis processing, for example as shown in FIG. 6(b), an edge emphasized value X is calculated with reference to the detected values a, b, c and d of the surrounding 4 pixels and according to an equation, for example, X=x-.alpha.(a+b+c+d-4x), wherein .alpha. is a predetermined coefficient.
Therefore, for the pixels on the joint portions in the subscannings the detected data of pixels obtained in the subsequent main scanning operation or in the immediately before main scanning operation are necessitated.
In FIG. 6(a), the blocks indicated by numerals 1 are first pixels and the blocks indicated by numerals 128 are last pixels for the CCD sensor 11, and for the above indicated reason as a memory for storing the detected values of these pixels, a line memory covering two line pixels along the main scanning direction (pixels on a main scanning line are defined as one line pixels) is incorporated in a device. Accordingly, at the moment when the detected values (pixel data) of the respective pixels are inputted which are obtained from the CCD sensor 11 at the subsequent scanning point (respective measurement points of the CCD sensor 11 along the main scanning direction), the one line before pixel corresponding to the pixel on the scanning point immediately before the subsequent scanning point (the detected value of the pixel is stored in the memory) is noted and the edge emphasis processing is performed for the noted pixel while referring to the detected values of the previous two line pixels stored in the line memory.
Namely, in order to edge emphasize the last line pixels and the first line pixels in the subsequent scanning operation, data on the scanning lines before and after the concerned line are necessitated. Therefore, data covering one scanning line have to be stored in the memory for the respective last and first line pixels, such that a line memory having a storage capacity covering at least two scanning line data has to be provided. The longer the width in the main scanning direction, the larger the capacity of the line memory. Further, the line memory has to be provided separate from an image memory, therefore the control thereof is also performed independent from that for the image memory. Accordingly, a separate control circuit therefor is necessitated.
In this type of scanners, the line memory is assembled into the CCD sensor so as to keep a required performance and to meet a required size reduction. However, when assembling the line memory, because of a limited room in the sensor portion there arise problems that the circuit assembling is difficult and the working therefor is lower. Further, due to such assembling the scanner itself becomes expensive as well as the size reduction thereof becomes difficult.